UART Interrupt on Rx

Hello, I apologize for such a stupid question - but I just don’t get it. I am also new to this board and these systems, so my experience is extremely limited.

What I want to do:

  1. SiFive Freedom U740 SoC board is connected to another microcontroller board using LPC1768, through UART 0 (on both ends)
  2. The LPC1768 will transmit UART data to the U740 board
  3. The U740 receives the data, by an interrupt
  4. U740 executes based on what data was received from UART

I can confirm that the LPC1768 is sending the data correctly, but I cannot wrap my head around accomplishing on getting the U740 to trigger an interrupt when it receives the data.

I took a look at this sample code, but I do not know what changes are required to trigger an interrupt on Rx. It seems that this code triggers on Tx.

freedom-e-sdk/software/uart-interrupt/uart-interrupt.c at master · sifive/freedom-e-sdk · GitHub

Can someone please shed some light on this?

Thank you and have a wonderful holiday!